Design of Ethernet switches in the optical fiber loop Industry

The ethernet switch technology has become more mature and stable. Because the Ethernet switches in the industry share many similarities with the switches we usually use, the design of the Industrial Ethernet switch also uses the principle of the commercial switch. With the rapid development of Ethernet technology and its wide application in the commercial field, more and more industrial control devices gradually use Ethernet and adopt TCP/IP Protocol as the main communication standard.

Although the Ethernet standards used in the industrial control field are the same as those for commercial Ethernet, in the industrial control field, networks must be able to work stably in harsh working environments. Therefore, network products used to connect industrial devices must be specially designed to provide industrial-level reliability to meet the needs of long-term continuous operation. In addition, in the industrial control field, the devices to be connected are scattered, with fewer devices to be connected in a single place, this requires a large number of fiber network switches that support eight ports of the fiber redundancy loop. To implement the optical fiber redundancy loop function, a high-performance microprocessor is required to implement network management and control functions, and a high-performance network switching chip is used to implement the Basic 10/100 M Ethernet Switching function. The following describes the software and hardware design ideas of an industrial Ethernet switch with 32-bit ARM Kernel microprocessor, six 10/100 M twisted pair ports, two M optical fiber ports, and a redundant loop function..

1. Hardware Design

The Optical Fiber Loop Ethernet switch hardware is divided into two modules: CPU module and switch module. The two modules are described in detail below.

1.1 CPU module

The CPU module can be divided into two parts, namely, the power supply part and the CPU and peripheral circuit part. The power supply must provide two channels, 10 ~ 40 v dc power supply, the two power supply backup each other, as long as one of the power supply is normal to make the system normal power supply. In addition, whether the two power supplies are normal is indicated by the two LEDs connected to the CPU. If the CPU finds an Abnormal road, it will drive the alarm indicator to indicate that the power supply is abnormal, and drive the relay to connect to another power supply. If the two channels are abnormal at the same time, because the alarm output of the relay is normally closed, the CPU has no output signal, and the contacts of the relay are closed, the alarm information can be provided to the remote end.

MAX788 is a switching voltage regulator. The output voltage of the regulator is 3.3 V, the maximum output current is 5A, and the input voltage range is 8 V ~ 40 V, internal switch frequency is 100 kHz. The CPU of the Ethernet switch is AT91M40800, the 32-bit ARM Kernel microprocessor chip of Atmel, and RAM uses the high-speed K × 16-bit SRAM CY7C1041BV33.

FLASH Memory 29W400 is used to save programs and some configuration information. Its capacity is KB × 16 bits. The serial port of AT91M40800 extends a RS-232 interface, and the PC directly manages and sets the Ethernet switch through the RS-232 port. MAX823 is a power monitoring chip with WATCHDOG function, providing reliable reset signals. The CPU module and the switching module are connected through a 40-core socket, which implements the register setting and network data read/write functions for the switching chip. The JTAG port implements Real-Time Simulation of AT91M40800 and downloads the program to FLASH memory.

1.2 switch Module

The switching module consists of the MAC layer master switching chip VT6510B and the Physical Layer Chip RTL8208. The main switch chip uses VT6510B produced by VIA. The chip has 9 10/100 M ports and 1g ports, and is embedded with KB of control RAM and Packet Exchange buffer RAM, complete switching functions can be implemented. In addition, host interfaces are provided to enable external CPUs to initialize and manage the switching chip.

The eight 10/100 M ports are connected to the Physical Layer Chip RTL8208 produced by Realtek through the RMII interface. The RTL8208 chip integrates eight physical layer ports, which can be configured to use 10/100 BASE-TX (twisted pair interface) or 100BASE-FX (optical fiber interface ). The system uses six 10/100 BASE-TX ports and two 100BASE-FX ports. The six 10/100 BASE-TX ports need to be connected to the RJ-45 interface through the isolation transformer HR604009, which is an isolation transformer that provides 4-way RJ-45 interfaces. Two 100BASE-FX ports can be directly connected to the optical transceiver V23826, which provides a single-mode SC interface.

In addition, the Physical Layer Chip RTL8208 can display the status of each network port through the serial shift register 74HC164 external LED Light Emitting tube output. Because the core operating voltage of VT6510B and RTL8208 is 2.5 V, the voltage of 3.3V must be reduced to 2.5 V by using a low-voltage regulator chip MAX1818.

2 Software Design

The main task of the vswitch software design is to set the registers of the switch chip VT6510B to realize the basic switching function; in addition, the host computer can set the switch through the RS-232 port or the network port on the Ethernet switch, to achieve the network port status monitoring, redundant loop, virtual LAN and other advanced management functions. According to the design requirements of the product, the software of the switch can be divided into the following parts:

(1) initialization

It mainly sets the initial values of various CPU registers and the initial values of each register of the switching chip, and starts the switch.

(2) network protocol

Implements 802.1d, 802.1 w, 802.1q, and PING, ARP, BOOTP, IP, TCP, UDP, and other network protocols.

(3) network management and function settings

Through the RS-232 port to achieve some basic parameters of the switch settings and status monitoring. In addition, based on the above network protocol, you can also directly set the parameters of the Ethernet switch and monitor the real-time status through the network.

(4) Fault Diagnosis and redundant loop implementation

Implement Fault Self-diagnosis and alarm for power supply and other parts of the Ethernet switch, implement the Protocol and policy according to the configured redundant loop, monitor the current connection status of the network and realize the self-healing function of the network. Due to the many similarities and differences between industrial Ethernet switches and common commercial switches, the principles of commercial Ethernet switches are referenced in the design, it also takes into account the characteristics of Industrial Ethernet devices. This design selects a powerful switching chip, network Physical Layer Chip and transceiver interface circuit, and uses a 32-bit embedded processor based on the ARM kernel to implement advanced network functions of the switch.